This is a problem I've never seen before. The head gasket failed on my 01 SS about 2 months ago. I replaced them, and all other gaskets. The car ran great for a few weeks, the I got a p0303. I checked all of the obvious ignition causes.. Switched plugs, wires and around and coils. Nothing worked! One day I was at a light and the car was shaking real bad and the CEL was flashing. I got to 2nd gear, floored it to hit the passing gear and let off... This somehow fixes the problem for about a week and it comes back, but if I floor it again the problem goes away every time. I don't like to drive a car rough with high miles (185K) let alone any car, but this is the only thing that works. I can really use some advice because I need to pass the Illinois emission test before the end of August to renew my plate sticker. It also needs a catalytic converter and an o2 sensor, but if I can't fix the misfire, why bother?


Any help would be highly appreciated! Sorry for the long post 😉

 

No one?

 

Swap the injectors around and see if the misfire moves. It might be trickling gas through and it not being enough, but then when you floor it and the PCM commands richer settings it opens a little more

 

I did that too, nothing made any difference so far.

 

One part of the ignition system you said nothing about is replacement ignition control module. They can be tested at Auto Zone. Heat kills them, especially if the heat sync lube is dried up between it and the coils.
But one thing I would be more suspicious of is a cracked head, intake manifold or block.
Here's a video by one poor SOB who over tightened the lower intake manifold on his 3400 and cracked it causing a P0303. Hope this isn't the case.

Video:

 

I've actually watched that video before. I didn't know Autozone would test the ICM. Do they test it while it's in the car?

Thanks for the reply

 

I've never had to do it, just heard of it being done.
I'm assuming Auto Zone does it because it seems like they can test everything else.
You might need to check with a auto-electric shop.